1. Field of the Invention
This invention relates to a socket having improved structural strength for burn-in and test of high lead count tape automated bonded very large scale integrated circuits (TAB IC devices) with closely spaced pads and in one aspect relates to an improved contact and contact mounting comb for improving and maintaining the alignment between each contact and associated tape pad.
2. Background of the Invention
The high lead count of TAB IC devices or leadless chip carriers formed of ceramic present unique problems in socket design since each contact must press against the TAB-test pad with a force high enough to insure reliable electrical contact. The force of all the contacts is additive and must be resisted by the strength of the socket. The socket must contain sufficient contacts to connect the TAB IC device to an external piece of electronic equipment. The socket must provide means to register the TAB IC device and carrier for accurate location, to control contact placement and deflection for contacting the test points, to accept thermal expansion variations without losing that contact, and to provide force at high enough levels to insure a reliable electrical connection through thermal cycling.
The prior art devices for test or burn-in of integrated circuit devices have many of the critical features of alignment, pressure contact with the pads, and a quad pack design. Examples of the socket configurations are illustrated in U.S.A. Pat. Nos. 4,378,139 and 4,553,805. These sockets for the IC devices are formed with contacts affording a wiping action on the test pads of the carrier and the registration is changed between the pad and the end of the contact when the carrier is pressed against the contact as the contact pivots during vertical movement of the carrier to press it against the contacts Further, the socket is not provided with any means of maintaining the contact during the temperature cycling which results in differential expansion of the TAB device, socket and contacts except the size of the contact and the pads.
The present invention is an improvement over existing sockets in that the contacts are formed to permit vertical movement of the pad contacting end, the contacts are mounted to restrict movement to a vertical direction and maintain sufficient strength to maintain good electrical contact, the combs supporting the contacts afford increased density between the contacts and pads, the combs are individually supported on the sides of the socket, the socket has a rigid support for the comb and expansion of the comb and movement of the contacts is limited to movement from the center of the comb to an end, the carrier is moved vertically and no horizontal component is introduced into the movement which causes a buckling of the TAB carrier either due to the movement of the contact or the swinging movement of the clamping or latching device, and the force applying mechanism is simplified and very easily operated to apply sufficient force against the carrier to make reliable contact with the multiple contacts.